Helicopter transmission mechanism



Aug. 11, 1953 w, TlDD 2,648,386

HELICOPTER TRANSMISSION MECHANISM Filed March 29, 1948 A TTORNE Y Patented Aug. 11, 1953 HELICOPTER TRANSMISSION MECHANISM Gage W. Tidd, Doylestown, Pa., assignor to Harris S. Campbell, Bryn Athyn, Pa.

Application March 29, 1948, Serial No. 17,645

7 Claims.

- This invention relates to transmission systems for helicopters and is particularly concerned with multiple speed units for driving helicopter rotors at difierent speed ratios.

In helicopters, it is desirable that during hovering operation the main rotor be driven at a comparatively slow speed of rotation in order to provide the greatest lift for a given amount of power. For example, rotational speeds which give rotor tipspeeds of from 350 to 450 ft./sec. are suitable. For high forward speed flight, it is desirable to have an increased tipspeed in order to prevent tip stall on the retreating blade which may cause undesirable vibration in the aircraft.

In many helicopters, an auxiliary rotor such as an antitorque tail rotor is used in addition to the main lifting rotor. The drive for this auxiliary rotor is normally coupled with the transmission for the main rotor in a fashion which permits the main rotor to drive the tail rotor during autorotational operation when engine power is removed. With a transmission having more than one speed ratio, it is desirable that full operational speed. on the auxiliary antitorque rotor be maintained during slow speed operation of the main rotor. The reason for this is that during this slow speed operation, the highest torque is developed by the main rotor and this torque mustv be overcome by the thrust of the auxiliary rotor. Therefore, full speed of the auxiliary rotor is desired at this time in order to develop its maximum thrust.

It is a primary object of the present invention to provide for the drive of such auxiliary rotors in a fashion which will allow maximum speed operation of the auxiliary rotor for slow speed operation on the main rotor and at the same time provide for suitable drive to the tail rotor during periods of autorotational operation of the main rotor.

It is an object of the present invention to provide in conjunction with a two speed transmission unit which is capable of transmitting torque in only one direction, during low speed operation, means for eliminating the speed reduction action of the unit during periods of reverse torque transfer. 7

A specific object of the present invention is the provision of an overrunning device in association with a two speed transmission for helicopters, which device operates under action of reverse torque from the main rotor, such as during autorotational operation or brake application. During such reverse torque drive the overrunning device becomes the medium for transmitting driving torque to the input shaft of the two speed unit and thereby provides the drive for the auxil-' iary rotor connected to this input shaft.

The present invention provides for the back drive features for an auxiliary rotor or the like as disclosed in the co-pending application of Harris S. Campbell, Serial No. 17,707, filed March 29, 1948, but accomplishes this back drive in certain specific ways.

How the foregoing and other objects and advantages of this invention are accomplished will be clear from the following description of the drawing in which Figure 1 is a side elevational view of an aircraft of the type to which the present invention is applicable.

Figure 2 is a side elevational view, partly in section, of a portion of a transmission system illustrating features of the present invention.

Figure 3 is a view of a portion of the two speed mechanism illustrating an alternate construction.

Figure 4 is a view of a portion of the two speed unit showing another form of construction.

In Figure 1 there is illustrated a single lifting rotor helicopter having a body ID with an cecupants compartment at I l in the forward portion thereof. A landing gear consisting of forward wheels l2 and rear wheel I3 is provided for support of the aircraft on the ground.

A sustaining rotor having a rotor hub 14 and rotor blades I5 connected thereto is attached to the fuselage ll]. During flight the rotor blades [5 are driven by means of the engine It through the medium of transmission units I! and I8. A shaft l9 connects the engine with the transmission unit and a drive shaft 20 transmits the power from the transmission unit ll to the tail rotor 2| which is mounted at the rear end of fuselage Ill.

The portion of the transmission unit indicated at [8 houses the main reduction gearing required to provide proper rotational speed for the rotor. A considerable reduction from the engine shaft speed is required, in many instances 10:1 or more reduction being needed, depending upon the size of the rotor.

In Figure 2, the portion of the transmission below the main gear reduction unit [8 is illustrated. This includes the two speed unit which is housed in the part of the transmission illustrated at ll. from external shaft 23 which may be driven from the engine through a suitable engageable clutch. Shaft 23 is supported in the lower end of the The drive to the transmission is gears 21 and 28, the latter of which is attached to take-off shaft 29.

Shaft 25 is the input or driving shaft for the two speed rotor under normal power operation.

When the two speed rotor is operating in low ratio condition, that is, when the two speed fric- Y tion clutch is in disengaged position, the-shaft- 25 drives the driven or output shaft of the two;

speed unit at a reduced'speed. This is accomplished through the mediumof the planetary gearing-consistingof theouter or driving gear shown at 3! attachedto shaft 25, the. inner gear shown at 32, and the planet gears-33 which are attached to a plate or spider 34 connected to driven shaft 30. During-this low speed operation,

the innerplanetary gearwhich -is the reaction gear, is heldstationar-y Withrespect tothe-housing 35 by means of an overrunning clutch .38. Thus, the-planetary gearing is effective to drive the output shaft 30 at a-speed which, in. the present gearing proportions, amounts to areduction of approximately 1.4 to 1. The upper end of driven shaft 30 1s supported in a bearing 3! and drives the main rotor through the medium of-the main reduction gearing, which is located-in the portion'of the housingshownatl8-in- Figure l.

Inorder-toflrive the output shaft 39 of the two speed unit=at" high speedratioythe friction clutch unit is engaged by means 'of lever 38 operating through thrust bearing 39.- The clutchwith its lever 38 as shown in full-line position, is in engaged position. (Here the plates 40' attached to'the outer-she1l4l which is connected to the-inner gear 132; are forced by means of compression springs 43 into frictional engagement with'plates fl whichare splined to driven shaft 30. During engagement of the clutch, the shaft to which gear 32 is connected is caused to rotate with'driven shaft 30=so that the planet gears are locked about their own axes with the result that direct 1 to 1 drive-is established between shaft-Hand shaft 30.- The overrunning clutch 36 permits forward oper--- ationof the gear shaft32.

Inorder'to return to slowspeed operation from high speed operation; the operator disengages the clutch by meansof suitable connections to-lever 38 and-:upon'movement of lever 38 to position 38a, the clutch isfully released permitting relative rotation of the two sets of discs. The gear reactions at 'the planetary gear set immediately cause stoppage of theinner gear 32 due to thereaction of overrunning clutch 36 against the housing, with the result that the transmission is. again returned the overrunning device 36 prevents transfer of this reversed torque. In order to provide for drive of the shaft 25 and the power take-01f 29, additional means must be provided to transfer this opposite torque. In the arrangement illustrated in Figure 2, an overrunning clutch 44 is located near the lower end of shaft 30, and reacting between it and the upper end of shaft 25 in a fashionsuch as when shaft' 25 tends tovoperate at a slower speed than shaft 30, the freewheeling unit 44 automatically becomes effective and provides for transfer of torque from shaft 30 to 'shaft 25. It will-baevident that upon resumption of-normaltorque, such as with the application of power, shaft 25 may increase its speed with respect to the speed of shaft 30 and drive -th-rough the p'l'anetary gearing since the clutch 25 to operate at speeds faster than shaft 30. Thus the continuedoperatiori of auxiliary drive-291$ assured" even-though f ailur'e' of "povlerto shaft 25 occurs. It Wil1"be"noted' that"overrunriifig unit 26 permits continued operation of shaft"'25 even.

though the power input shaft"23fromtliehgine may be stopped or operatingatflow speed. Rotor brake is' on shaft 29. i

"In Figure 3, a somewhat difierent' arrangement' is provided -for" obtaining the driveback through the twospeed i'mittoth'e auxiliary rotor take-off. The two speed mechanism fs"essentiallythe same as in the cas'epf'Figurazflbeing composed of the planetary "geaftraimimembers 3|,"32 and 33) with the overrunningrea'ction clutch 35 between gear 'meml'ier '32 andhdusing. To provide for the" reversed'tordue foperation, an additional 'overrunning unit 4'5-i s .Iocatedbetween the'output'or driven -sha'ft 30 andthe reaction gear member 32. Overrunning Iclutch 5 is arrangedt'o operate to preventigeafmember 32 from 'runningfiforward ata "speed' irfiexcess of the speed of output shaft =s'ul wne'n' the torque is reversed from thelnormal driving direction; shaft 30tends to drive ,babkthrou'gh'the planetary gearingto drive shaft '25."'However,

in so doing, the reactions at thege'a'rs 33 and 32 are reversed withthe effect that gar32 tends to rotate in the'samedirecti'on asrshaft30, this being permitted by overrunnifigclutch 36. Overrunning clutch "45,""howeverfprevents the speed of gear member 32zfrom' exceeding the speed'of shaft '30, with theresult thatsh'aft'fll can drive back through the planetaryfgearsym tem at a 1 to 1 ratio,thus driving-shaft15so that power can be transmitted-to theauidliary take-off.

Figure" 4 shows another method or roviding for the transmission 'of'revfersed torquethrough the planetary reduction system "when'iit' is conditioned for low speed operation, 'thatis;"when the two speed clutch unit is disengaged. flIn this case, the same 'general arrangemnt for gearing may be used, involving driving gear '48, planet gears 41 and reaction gear member 48. The reaction overrunn'ing' clutch between gear member"48 vand thehbusing'is"indicated at '49. Thus the driving shaftlifl canw'ransmir torque to the driven shaft 5|, the latter being fd'rlven at 'a slower speed thanshaft 501" Under the condition of reversed torque such as during'autorotational operation or application "of the "rotor brake, while the direction of rotation continues the same,.shaft '5! tendstd drivjshaft '50. This wouldcause anfoverdrive' t'obccur on the reaction gearmember- 48} and due to overruiining clutch 49, such overspeediiig"coi1ldoccur'unrestricted, thus preventing effective transmission of torque from shaft 5| to shaft 50. As shown in Figure 4, an overrunning clutch member 52 is supplied in association with each planet gear 47. This overrunning clutch is arranged to allow the planet gears 41 to rotate in a forward direction such as required during normal powered drive when shaft 50 is driving shaft 5| at reduced speed. Upon reversal of torque, when the tendency is to overdrive reaction gear member 48, a reversal in the direction of rotation of planet gears 41 on their own axes would normally occur. The overrunning clutches 52 which react between axle members 53 and the gears 41, prevent such reversed rotation of gears 41 from occurring, thus in effect locking the gears during reverse torque operation. This locking produces a 1 to 1 drive relationship when shaft 5| tends to drive shaft 5!]. Thus shaft 50 may effectively transmit the power necessary for operation of the auxiliary rotor driveshaft which is connected to shaft 5|] during autorotation and rotor braking operations.

From the above description, it will be clear that I have provided a simple means for transmission of reverse torque through a helicopter multiple speed unit. With the arrangement of the main overrunning device which permits the transmission and rotor to freewheel with respect to the engine driving shaft in case of engine failure, and the use of a freewheeling reaction device in connection with the two speed unit, the provision of additional freewheeling means is used to permit driving of the shaft, which is normally the input shaft, from the rotor side of the two speed unit. By placing the third overrunning means in proper position with respect to the members of the planetary transmission, or with respect to the input and output shafts, an unusually simple and satisfactory means for supplying the needed power for operation of auxiliary drives in proper fashion, is provided.

I claim:

1. A helicopter having a sustaining rotor, a power plant, said rotor being capable of being operated either from said power plant or by aerodynamic actuation during flight, a transmission system between said power plant and said rotor including a drive from the power plant having a freewheel clutch to permit the rotor to continue operation under aerodynamic forces upon reduction of the engine speed below rotor operational speed, a two speed transmission unit including a housing, planetary gearing, an input shaft to said two speed unit normally driven by said power plant through said freewheel clutch, auxiliary rotor take-off gearing connected to said input shaft, an output shaft from said two speed unit to said rotor, a second freewheel device engaging said housing and an element of said two speed unit and arranged to transmit a uni-directional torque therebetween to cause operation of said planetary gearing to drive said output shaft at a reduced speed, and a third freewheel device engaging said input shaft and an element of said two speed unit and arranged to transmit a uni-directional torque therebetween to cause drive of said input shaft when said output shaft is being driven by said rotor.

2. A helicopter having a sustaining rotor, a power plant, said rotor being capable of being driven either by said power plant or by aerodynamic forces during flight, a transmission system between said power plant and said rotor including a two speed unit to permit drive of 6 said rotor by said power plant at different speeds, said. two speed unit having input and output shafts, planetary gearing interconnecting said shafts to provide low speed drive of the sustaining rotor, a housing, a freewheel device reacting between an element of said planetary gearing and said housing to provide for operation of the gearing when being driven in low ratio, an auxiliary drive take-off connected to the input shaft, a second freewheel device located between the power plant and said input shaft and a third freewheel device reacting between two elements of said two speed unit to provide unidirectional drive from said output shaft to said input shaft upon reversal of normal driving torque when said rotor is being aerodynamically driven.

3. For a helicopter having a sustaining rotor and a power plant, a two speed transmission device having a housing, an input shaft from the power plant and an output shaft to the rotor, planetary gearing interposed between said shafts, a freewheel device reacting between said gearing and said housing when being driven by said input shaft, a second freewheel device reacting directly between said shafts when said output shaft is driving said input shaft, a third freewheel device located in said input shaft to permit said transmission to overrun said power plant and an auxiliary rotor drive connected to said input shaft between said second and third freewheel devices.

4. For a helicopter having a sustaining rotor and a power supply, a two speed transmission having a housing, input and output shafts, planetary gearing including a reaction gear member and a planet gear, a freewheel device reacting between said member and said housing during drive from the input shaft, a second freewheel device reacting between said output shaft and another part of said transmission during drive from the output shaft, a third freewheel device located in said input shaft to permit a portion of said shaft to overrun said power supply, and an auxiliary rotor drive connected between said second and third freewheel devices.

5. A helicopter having a sustaining rotor, a power plant, said rotor being operable either by said power plant or by aerodynamic actuation during flight, a transmission system between said power plant and said rotor including a drive from the power plant having a freewheel clutch to permit the rotor to continue operation under aerodynamic forces upon reduction of engine speed below operational speed, a two speed transmission including a housing, a planet gear, a planet gear support, a sun gear, an input shaft to said two speed unit normally driven by said power plant through said freewheel clutch, an auxiliary rotor power take-off connected to said input shaft, an output shaft from said two speed unit to said sustaining rotor, a second freewheel device reacting between said sun gear and said housing to cause operation of said output shaft at reduced speed, and a third freewheel device engaging two elements of said two speed unit and arranged to transmit unidirectional torque therebetween in a direction to provide drive from said output shaft to said input shaft.

6. A construction in accordance with claim 2 in which the planetary gearing incorporates a reaction gear member and in which the first mentioned freewheel device reacts between the reaction gear member and the housing.

7. A construction in accordance with claim 2 

